1. Field of the Invention
This invention relates to planar, flexible film air pallets, and more particularly, to an improved low cost air pallet employing thin flexible film sheet material.
2. Description of the Prior Art
Recently, flexible film air pallets have come into vogue to permit relatively heavy loads to be transported across fixed, horizontal support surfaces, with minimal frictional restrain due to the air bearing existing between the pallet and that support surface. U.S. Pat. No. 3,948,344 issuing Apr. 6, 1976, to Raynor A. Johnson and William D. Fletcher and entitled "LOW COST PLANAR AIR PALLET MATERIAL HANDLING SYSTEM" is representative of such air pallets.
The present air pallet constitutes an improvement within this art. The air pallet of U.S. Pat. No. 3,948,344 may take the form of a single flexible film sheet which is fixed about its edges directly to a load and being perforated within an area lying beneath the load with air inlet means to one side of the film sheet and with air dispersion means incorporated within that structure to insure distribution of the air entering the inlet to all areas beneath the load for discharge through the multiple perforations within the flexible sheet.
In addition to the air dispersion means, it is necessary to provide means to insure jacking of the load, that is, raising of the load some vertical distance from the fixed support surface and the creation of the plenum chamber, all without ballooning of the air pallet and resultant tipping or excessive tilting of the load. A portion of the flexible film sheet at the edges of the load is preferably non-perforated such that initially with the load pressing the perforated portion of the flexible film sheet against the fixed support surface, in order for the air to escape, the load must be jacked to the extent that some edge perforations are exposed, that is spaced some distance from the fixed load support surface. The air escapes, at which point an equilibrium "jacked" position is reached where the load is supported several inches above the fixed support surface on an air film created between the loaded pallet and the fixed support surface. The load may then be moved frictionlessly horizontally relative to the fixed load support surface regardless of minor variations in contour, surface roughness or the like, both with respect to the fixed support surface and the load or air pallet.
Additional embodiments of the invention in U.S. Pat. No. 3,948,344 are directed to air pallets where a flexible film bag functions as the primary member of the air pallet, and is affixed to the lower surface of the load and bears perforations on the bag wall immediately facing the fixed load support surface, with an integral tube, extending from the side of the air bag and being coupled to a wand through which air under pressure is directed to pressurize the plenum chamber formed by the bag. In such cases, either internally or externally, air dispersion means must be provided to insure the distribution of air throughout the plenum chamber to accomplish jacking of the load and permit air escape through the perforations to define the air bearing for the air pallet supported load.
While the air pallet employing the flexible film sheet as a single layer of a laminated air pallet structure or where dual flexible sheets in the form of an air bag such as a plastic garbage bag may function totally to define the air plenum chamber for the air pallet, certain problems arise particularly where the flexible film sheets are relatively fragile. First, where the bag or similar structure terminates in an integral tube which is coupled in turn to a vacuum cleaner wand or similar metal tubular structure acting as a conduit for the air under pressure from a pack carried or vehicle carried compressed air source, there is a tendency for the air bag or flexible sheet to tear as a result of air-pressure induced stress occurring at the line of juncture between the tube or air inlet portion of the flexible film sheet or bag and the main portion of the film or sheet defining the plenum chamber. Secondly, where the air inlet opens to the air bag or flexible film sheet portion defining wholly or partially the plenum chamber, the jacking of the load and pillowing of the air bag or flexible film sheet portion of the air pallet has resulted in the tilting of the load in a direction towards that portion which is still pressed into contact with the relatively fixed load support surface, causing the load to be dumped from the air pallet. In addition, this increases severely the stress to the portion of the air pallet partially filled with air at relatively high pressure, particularly in the area of the inlet to the flexible film sheet or air bag.
Where the inlet tube to the flexible film sheet or to the air bag abuts directly a load bearing area, that is, opens up into a plenum chamber which is completely closed due to the press of the load on the surface area of the bag or flexible film adjacent the air inlet, jacking of the load in many cases simply cannot be achieved.
Further, it is under these circumstances, that there is a great tendency due to the high air pressure and zero flow conditions for the bag or flexible film sheet to rupture at the area where the air enters the same, particularly where the bag or flexible film sheet is provided with an integral tube acting as an air inlet to the plenum chamber.